The overwhelming majority of microelectronic devices in current use are based on silicon technology. However, more and more microelectronic devices are being based on silicon germanium (SiGe) technology. Silicon germanium technology has numerous advantages. Silicon germanium technology is capable of providing higher operating speeds, lower levels of noise, lower levels of power consumption, and higher levels of integration. Silicon germanium technology is currently being employed in wireless radio frequency (RF) integrated circuits.
In a silicon germanium (SiGe) integrated circuit the combination of silicon and germanium improves the electrical properties of the integrated circuit. For example, the addition of germanium to a silicon bipolar transistor improves the operating frequency, current, noise, and power capabilities of the transistor.
Silicon germanium (SiGe) technology is also being employed in the manufacture of BiCMOS films. BiCMOS is an integrated circuit technology that incorporates bipolar (Bi) semiconductor devices and complementary metal oxide (CMOS) semiconductor devices on the same integrated circuit die.
During the manufacture of a BiCMOS film it is important to be able to determine how much germanium (Ge) is present in a silicon germanium film. If too much or too little germanium is used in the silicon germanium film then the film will not have the desired operating characteristics. In order to provide quality control of the manufacturing process it is necessary to measure the germanium concentration during the manufacturing process.
A number of prior art methods exist for measuring the concentration of germanium in a silicon germanium film. A first prior art method involves monitoring the germanium concentration using a secondary ion mass spectrometer (SIMS). A second prior art method involves monitoring the germanium concentration using high resolution X-ray diffraction (HRXDF). A third prior art method involves monitoring the germanium concentration using Raman spectroscopy. A fourth prior art method involves monitoring the germanium concentration using a spectroscopic ellipsometer (SE).
These prior art methods have significant drawbacks. The prior art methods tend to be relatively expensive and must be performed by a highly qualified engineer. Some of the prior art methods require considerable time to perform. For example, the SIMS method can take up to three (3) days to perform. In addition, the prior art methods usually require the services of an external analytical laboratory in order to obtain the desired germanium concentration measurements. The prior art methods can not detect deviations in the germanium concentration in a real time manner or provide a measurement of the germanium concentration in a silicon germanium film in a real time manner.
Therefore, there is a need in the art for a system and method for measuring a germanium concentration in a semiconductor wafer for manufacturing control of a BiCMOS film. There is a need in the art for a system and method for making inexpensive real time measurements of germanium concentration in order to detect process deviations of a germanium concentration in a real time manner.